This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2001-12122, filed Jan. 19, 2001; No. 2001-282276, filed Sep. 17, 2001; and No. 2001-398384, filed Dec. 27, 2001, the entire contents of all of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a current perpendicular to plane type magnetoresistive device, a magnetic head including the current perpendicular to plane type magnetoresistive device, and a magnetic recording/reproducing apparatus employing the magnetic head.
2. Description of the Related Art
In recent years, magnetic recording apparatuses such as a hard disk drive and so on have been made more compact and more highly dense rapidly, and it is forecasted that they will be made further more highly dense. In order to attain high density in magnetic recording, it is required to increase recording track density by narrowing a recording track width, and also to increase longitudinal recording density, i.e., linear recording density.
However, in in-plane longitudinal recording, the higher the recording density, the larger the diamagnetic field, and therefore reproduction output is decreased and stable recording cannot be made, which has been problems for the prior art. To solve these problems, perpendicular recording is proposed. In the perpendicular recording, a recording medium is magnetized in a perpendicular direction to its plane and thereby recording is carried out. The perpendicular recording is subjected to less influence of diamagnetic field even when recording density is increased compared with the longitudinal recording, which makes it possible to prevent reproduction output from deteriorating.
Conventionally, in both longitudinal recording and perpendicular recording, an inductive head has been employed for reproducing medium signals. However, when the recording track width is narrowed along with high density and the recorded magnetization becomes small, it is difficult to obtain sufficient reproduction signal output with the inductive head. Therefore, so as to attain sufficient reproduction signal output even when the recorded magnetization becomes small, an anisotropic megnetoresistive (AMR) head with high reproduction sensitivity employing an anisotropic megnetoresistance effect has been developed, and used as a shield type reproducing head. In recent years, a spin valve type giant magnetoresistive (GMR) head with higher sensitivity employing a giant magnetoresistance effect has come to be used.
Further, research and development toward practical applications of magnetic heads using tunneling magnetoresistive (TMR) device and current perpendicular to plane (CPP)-GMR device with expectations of still higher reproduction sensitivity are promoted. In these devices, a sense current is flowed in a perpendicular direction to film plane thereof. The CPP-GMR devices are disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 10-55512 and U.S. Pat. No. 5,668,688. In this way, magnetic heads with high reproduction sensitivity have been developed, and, by using them, it has become possible to reproduce recorded signals even when recording bit size becomes extremely small.
So as to increase linear recording density in a recording track, it is necessary to narrow a gap of a magnetic head. In a conventional magnetic head using magnetoresistance effect, a magnetoresistive device is formed in a head gap defined by the space between a pair of shields. In both AMR head and spin valve GMR head, the thickness of a magnetoresistive device must be about 30 nm, and, taking into consideration of insulation with shields, the space between shields must be about 100 nm. In this way, the range where the head gap can be narrowed is limited to about 100 nm for the conventional magnetic head, which has been a large obstacle in increasing linear recording density. In order to realize a narrow gap under these circumstances, proposed is a device having a structure that a flux guide is formed on the air-bearing surface side and a sensing portion is recessed from the air-bearing surface. Especially, in a CPP-GMR device, it is required to arrange a GMR device and a pair of upper and lower electrodes between shields, and the thickness of these members becomes a great restriction to the narrow gap. Accordingly, in order to attain narrow gap in a CPP-GMR device, it is effective to form a flux guide on the air-bearing surface side and recess the electrodes from the air-bearing surface, thereby disposing a thin flux guide only between shields on the air-bearing surface.
So as to suppress Barkhausen noise in a magnetoresistive film, it is effective to arrange biasing films on both sides of the magnetoresistive film and apply a biasing magnetic field. However, the present inventors have found that when the distance between biasing films is narrowed along with narrow track for improving recording density, the biasing magnetic field is applied to the magnetoresistive film too strongly, as a result magnetization reversal becomes hard, which brings about a problem of deteriorating the device sensitivity.
In the conventional current in plane (CIP)-GMR device in which a sense current is flowed through the film plane, an operating point are determined by balancing three magnetic fields, namely, a current magnetic field generated by a sense current, a magnetostatic coupling magnetic field from a pinned layer to a free layer, and an interlayer coupling magnetic field between a pinned layer and a free layer. However, in a device in which a sense current is made to flow in a perpendicular direction to the film plane thereof, since the sense current magnetic field is applied in a circular form around the center of the current, it is impossible to use the designing scheme for determining the operation point mentioned above. Further, since the sense current magnetic field acts most strongly at the edge portions of the electrodes for supplying the sense current, the medium flux is disturbed to be introduced into the magnetoresistive film under the electrodes as a sensing area, which leads to declined sensitivity of the sensor.
These problems have not been pointed out in the abovementioned Jpn. Pat. Appln. KOKAI Publication No. 10-55512 and U.S. Pat. No. 5,668,688, and therefore these documents do not suggest a solution to the problems.
To solve the above problem that sensitivity of the device is deteriorated when the distance between the biasing films is narrowed, the distance between the biasing films may be made apart in some measure so that the distance between the electrode and the biasing films may be made apart. However, in a CPP-GMR device, there is also found a problem that when a physical track width defined by the electrode width becomes smaller than about 0.3 xcexcm, the effective track width becomes wider than the physical track width. This phenomenon is made more significant in structures where the distance between the electrode and the biasing films is long. As one of causes of this problem, it is considered that the medium flux is introduced into the magnetoresistive film located between the electrode and the biasing films. From these causes, it is difficult to attain a desired effective track width, and to cope with a narrow track width.
The abovementioned problem that the current magnetic field prevents introduction of the medium flux becomes more significant when the recording density becomes higher, namely when the size of the magnetoresistive device as a sensor and the electrode becomes smaller. For example, when the electrode size is made smaller than 1 xcexcmxc3x971 xcexcm to implement a recording density exceeding 100 Gbpsi, the medium flux is prevented from being introduced into the magnetoresistive film under the electrode. When the electrode size is made small, in particular, since it is necessary to flow a high sense current so as to obtain a certain level of output, the problem mentioned above becomes serious.
As practical examples, four types of CPP-GMR devices each having following (electrode size, GMR film size) were fabricated, respectively: (0.5 xcexcmxc3x970.5 xcexcm, 1.2 xcexcmxc3x971.2 xcexcm), (0.3 xcexcmxc3x970.3 xcexcm, 0.7 xcexcmxc3x970.7 xcexcm), (0.2 xcexcmxc3x970.2 xcexcm, 0.5 xcexcmxc3x970.5 xcexcm), and (0.1 xcexcmxc3x970.1 xcexcm, 0.3 xcexcmxc3x970.3 xcexcm). A sense current of 5 mA was applied to each CPP-GMR device, and the flux density distribution in the GMR film was examined under the state that the sense current magnetic field is applied. As a result, in the CPP-GMR device having (electrode size, GMR film size) of (0.5 xcexcmxc3x970.5 xcexcm, 1.2 xcexcmxc3x971.2 xcexcm), the flux density in the GMR film was sufficiently small. As the electrode size became smaller, however, it was found that the flux density in the GMR film became significantly strong on the edge portions of the electrode compared with other portions. FIG. 1 shows a relationship between the electrode size and the maximum flux density in the GMR film on the edge portions of the electrode. FIG. 2 shows a relationship between the sense current and the maximum flux density in the GMR film on the edge portions of the electrode of the CPP-GMR device having (electrode size, GMR film size) of(0.1 xcexcmxc3x970.1 m, 0.3 xcexcmxc3x970.3 xcexcm).
Considering all the various results together, in the case where the electrode size is 0.3 xcexcmxc3x970.3 xcexcm or less and the sense current value is 1 mA or more, and particularly in the case where the electrode size is 0.1 xcexcmxc3x970.1 xcexcm or less and the sense current value is 3 mA or more, it is required to take countermeasures so that introduction of the medium flux into the GMR film under the electrode should not be prevented so as to increase the sensitivity of the sensor.
In magnetic recording apparatuses such as a hard disk drive and the like, as high recording density progresses, a flying height that is a distance between the magnetic head and the recording medium is gradually lowered. Such decrease in flying height means that there is an increasing possibility of head crash with minute protrusions on the recording medium, and thermal asperity (TA) noise becomes an actual problem. Therefore, it is preferable to adopt a yoke type head configuration in which the medium flux is introduced into the magnetoresistive device via the yoke so that the magnetoresistive device should not be exposed to the air-bearing surface. Among yoke type magnetic heads, a horizontal yoke type magnetic head, in which the magnetoresistive device is arranged with its film surface in parallel with the air-bearing surface, is advantageous because the structure enables to arrange the whole magnetoresistive device near to the medium. Even in such a yoke type magnetic head, there is a problem that the sensor sensitivity is decreased when a strong biasing magnetic field is applied or a strong sense current magnetic field is applied. Accordingly, it is preferable to increase the sensitivity of the sensor.
Accordingly, an object of the present invention is to provide a current perpendicular to plane type magnetoresistive device that enables to decrease influences of a current magnetic field and a biasing magnetic field, thereby improving sensitivity, a magnetic head including the current perpendicular to plane type magnetoresistive device, and a magnetic recording/reproducing apparatus employing the magnetic head.
A current perpendicular to plane type magnetoresistive device according to one aspect of the present invention comprises: a magnetoresistive film; a pair of electrodes which allow a sense current to flow through the magnetoresistive film in a perpendicular direction to film plane; and a biasing film which imparts a biasing magnetic field to the magnetoresistive film in a parallel direction to film plane; wherein the direction of the magnetic field generated by the sense current flowing through the magnetoresistive film in the perpendicular direction to film plane is made substantially anti-parallel to the direction of the biasing magnetic field in a vicinity of a portion of the magnetoresistive film where a signal magnetic flux is introduced.
A current perpendicular to plane type magnetoresistive device according to another aspect of the present invention comprises: a magnetoresistive film; a pair of electrodes which allow a sense current to flow through the magnetoresistive film in a perpendicular direction to film plane; a biasing film which imparts a biasing magnetic field to the magnetoresistive film in a parallel direction to film plane; and a magnetic film disposed in a vicinity of a portion of the magnetoresistive film where a signal magnetic flux is introduced to the magnetic film; wherein the direction of the magnetic field generated by the sense current flowing through the magnetoresistive film in the perpendicular direction to film plane is made substantially anti-parallel to the direction of the biasing magnetic field in the magnetic film.
The magnetic film disposed on the side of the magnetoresistive film where a signal flux is introduced functions as a flux guide that guides the signal flux into the magnetoresistive film. This magnetic layer may be the whole magnetoresistive film, or a magnetic layer formed by extending only a free layer of the magnetoresistive film to the air-bearing surface side, or a soft magnetic layer of NiFe or the like arranged separately from the magnetoresistive film.